1. Bring a pot of salted water to a boil. Cook pasta until al dente, about 10 minutes or as package label directs.
2. Melt butter in a large skillet over medium heat. Add leek and cook, stirring often, until softened, about 3 minutes. Add peas and half-and-half and bring to a boil over high heat. Reduce heat to low and simmer until thickened, about 5 minutes. Stir in ham. Season with salt and pepper.
3. Drain pasta, reserving 1/2 cup cooking water. Add pasta to skillet along with cheese and toss to coat, adding cooking water as necessary to moisten. Serve immediately with extra Parmesan on the side.